1. Field of the Invention
The present invention relates to the production of an improved particulate urea product, normally in granular form, having both eminently improved anticaking and hardness characteristics. The modus operandi of the instant invention follows the second embodiment discussed supra in the introduction thereof, to wit, directly or indirectly incorporating into the urea melt certain new, novel, and heretofore unknown additive materials (unknown in the sense that these materials, although commonly available, have heretofore been unrecognized as having desirable characteristics of imparting to the formed urea particles the improved characteristics realized by practice of the instant invention).
2. Description of the Prior Art
As noted above, numerous investigators have discovered, taught, and disclosed a plethora of conditioning agents which may be added either directly to the anhydrous molten urea melt or indirectly thereto by means of incorporating same into the synthesis liquor before said melt is processed to the particulates formed therefrom to either improve the anticaking characteristics; the nonfriable characteristics; and/or, allegedly in some instances, improvements in both of these areas. These problems, as well as other attendant considerations for storage, handling, and application characteristics of granular/particulate urea, have been alleviated, to a significant degree, by the addition to the urea melt of low concentrations, e.g., 0.1 percent to 0.5 percent, by weight, of formaldehyde, which formaldehyde reacts with the urea to form urea-formaldehyde addition products. It has long been known that these addition products or compounds act to modify the crystallization pattern of the substantilly anhydrous molten urea during the subsequent formation thereof into solid particles by prilling, granulation, or other means to effect the production of substantially harder, abrasion-resistant particulates. Of particular interest from the practical aspects of this approach for methods employing the addition of formaldehyde, are those taught in the following references: Allgeuer and Weintrotter, U.S. Pat. No. 3,112,343, Nov. 26, 1963; Van Hijfte et al, U.S. Pat. No. 4,160,782, July 10, 1979; and Elstrom et al, U.S. Pat No. 4,204,053, May 20, 1980. Perusal of the above references reveals teachings of the formation of various concentrated solutions of a urea-formaldehyde reaction product(s) which are subsequently added in predetermined and desired amounts to the urea synthesis liquor, either before or after concentration thereof, or to the essentially anhydrous molten melt prior to ultimate formation of the desired particulate urea.
Although many of the problems associated with friability and caking of such formed particulate urea may be alleviated, as indicated above, to a significant degree by the addition of such relatively low concentrations of principally formaldehyde to either the urea synthesis liquor or the essentially anhydrous molten melt, modern day health and safety considerations under the genesis of modern environmental concerns have led or are presently leading to the close scrutiny of the many chemicals, organic as well as inorganic, utilized in the fertilizer-food chain. It is my understanding that formaldehyde is now designated as a toxic and/or carcinogenic material by the U.S. Environmental Protection Agency (EPA) which designation may well lead to either the restriction or total prohibition of the use of formaldehyde in agriculture products, including its use as a conditioning agent in the preparation of urea for fertilizer or animal feed preparation purposes.